Proper validation of empty string value in identity_type

[viliampucik]

This is continuation of #1978.

Because the logical operators (||, &&) in Terraform do not short-circuit, and coalesce() never returns non-empty string, empty string validation needs to be done differently.

The provided code change properly validates if identity_type is null or empty string or any of the allowed keywords.

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Checklist

I applicable, I acknowledge that I have:

• Read the contributing guide
• Ran terraform fmt on all modified files
• Regenerated the relevant README.md files using tools/tfdoc.py
• Made sure all relevant tests pass

[ludoo]

Thanks for this.

Nit: I did not check but from memory contains([null, "", ...]) might also work.

[viliampucik]

contains() would fail if its last argument would be null:

contains([null, "", "a", "b"], null)
╷
│ Error: Invalid function argument
│
│   on <console-input> line 1:
│   (source code not available)
│
│ Invalid value for "value" parameter: argument must not be null.

[ludoo]

contains() would fail if its last argument would be null:

contains([null, "", "a", "b"], null)
╷
│ Error: Invalid function argument
│
│   on <console-input> line 1:
│   (source code not available)
│
│ Invalid value for "value" parameter: argument must not be null.

Thanks for correcting me, you're absolutely right :)